The semiconductor integrated circuit industry has experienced rapid growth over the past several decades. Technological advances in semiconductor materials and design have produced increasingly smaller and more complex circuits. These material and design advances have been made possible as the technologies related to processing and manufacturing have also undergone technical advances. In the course of semiconductor evolution, the number of interconnected devices per unit of area has increased as the size of the smallest component that can be reliably created has decreased.
Semiconductor fabrication relies heavily on the process of photolithography, in which light of a given frequency is used to transfer a desired pattern onto a wafer undergoing semiconductor processing. To transfer the pattern onto the wafer, a photomask is used. The photomask permits and prevents light in a desired layout onto a layer of the wafer, such as a photoresist (PR) mask, which chemically reacts to the light exposure to remove some portions of the PR mask and leaving other portions. The remaining PR mask is then used to pattern an underlying layer, which sometimes is used to pattern another underlying layer. As feature sizes have decreased, the wavelength of light used in photolithography to pattern mask layers has decreased as well, creating additional difficulties and necessitating technological advances such as the use of EUV as a light source, phase-shifting masks, and other advances.
In some instances, multiple masks may be used to form the features of a single desired layout. Each of the multiple masks is used to create different features contained within the desired layout. However, using multiple masks to achieve a single layout can be problematic. If two adjacent features, each from a different submask, are formed too close to each other unwanted electrical connections may be formed or desired connections may not be formed. Some processes, such as self-aligned double patterning (SADP) attempt to remedy such problems, but attempts to do so by introducing a number of constraints.
Thus, the current techniques have not been satisfactory in all respects.
These figures are better understood by reference to the Detail Description included below.